1. Field of the Invention
The present invention relates to an electromagnetic wave detecting element. In particular, the present invention relates to an electromagnetic wave detecting element that includes a TFT active matrix substrate that detects an image and at which sensor portions are provided in correspondence with intersection portions of plural scan lines and plural signal lines that are disposed so as to intersect one another.
2. Description of the Related Art
Radiation image detection devices such as FPDs (flat panel detectors), in which an X-ray sensitive layer is disposed on a TFT (thin film transistor) active matrix substrate and that converts X-ray information directly into digital data, and the like have been put into practice in recent years. As compared with a conventional imaging plate, an FPD has the advantages that an image can be confirmed immediately and video images as well can be confirmed, and the popularization of FPDs has advanced rapidly.
Various types of such a radiation image detection device have been proposed. For example, there is a direct-conversion-type radiation image detection device that converts radiation directly into charges and accumulates the charges. Moreover, there is an indirect-conversion-type radiation image detection device that once converts radiation into light at a scintillator of CsI:Tl, GOS (Gd2O2S:Tb), or the like, and, at semiconductor layer, converts the converted light into charges and accumulates the charges (see, for example, Japanese Patent Application Laid-Open (JP-A) No. 2000-137080).
As an example, a plan view showing the structure of one pixel unit of an electromagnetic wave detecting element 10′ that is used in an indirect-conversion-type radiation image detection device, is shown in FIG. 13. Further, a cross-sectional view along line A-A of FIG. 13 is shown in FIG. 14.
As shown in FIG. 13, sensor portions are provided at the electromagnetic wave detecting element 10′, in correspondence with the respective intersection portions of plural scan lines 101′ and plural signal lines 3′ that are disposed so as to intersect one another.
As shown in FIG. 14, the sensor portion includes: a semiconductor layer 6′ at which charges are generated due to light being illuminated; an upper electrode 7′ that is formed by a light-transmissive, electrically-conductive member at an illumination surface side of the semiconductor layer 6′ at which light is illuminated, and that applies bias voltage to the semiconductor layer 6′; and a lower electrode 14′ that is formed at the light non-illumination surface side of the semiconductor layer 6′, and collects charges that are generated at the semiconductor layer 6′.
At the electromagnetic wave detecting element 10′, common electrode lines 25′, that supply bias voltage to the upper electrodes 7′, are disposed at the upper layer of the semiconductor layer 6′. The resistance of the common electrode lines 25′ must be made to be low in order to supply charges. Therefore, the common electrode lines 25′ are formed by using a low-resistance wiring material of Al or Cu, or of mainly Al or Cu.
U.S. Pat. No. 5,777,355 discloses a technique of connecting respective upper electrodes that are formed from transparent, electrically-conductive members, so as to have them function also as common electrode lines.
However, as shown in FIG. 14, if the common electrode lines 25′ are disposed at the illumination surface sides of the semiconductor layer 6′, light is not illuminated onto the portions of the semiconductor layer 6′ beneath the common electrode lines 25′, and the efficiency of utilizing light decreases.
Thus, an electromagnetic wave detecting element that, by using the technique disclosed in U.S. Pat. No. 5,777,355, connects the respective upper electrodes 7′ that are formed from transparent, electrically-conductive members and causes them to function also as common electrode lines, is considered.
However, usually, the resistivity of a transparent, electrically-conductive member is very large, and is 50 to 200 times that of a low-resistance wiring material. Accordingly, if the upper electrodes 7′ are respectively connected and made to function also as common electrode lines, the wiring load (resistance, capacity) of the common electrode lines increases, and the desired response cannot be realized. Therefore, the upper electrodes 7′ cannot be respectively connected and made to function also as common electrode lines.
Note that, in the above description, the efficiency of utilization of light is mentioned because light is the object of detection of the semiconductor layer 6′. However, such problems arise as well in cases in which the object of detection is any type of electromagnetic waves such as ultraviolet rays or infrared rays.